Electromagnetic and/or electrohydraulic forming of a metal plate

ABSTRACT

A metal plate is formed in a process comprising cutting, perforating or both, by forcing the plate, by means of an abrupt and intense force towards a mold having openings or boundaries defined by wall sections which extend essentially normal to the forming plane of the mold. Consequently, the plate is cut along the edges of the openings or boundaries. The force may be a pulsed magnetic force or may be a force generated as a result of the discharge of electric current through a fluid.

REFERENCE TO RELATED APPLICATIONS

The present application is the national stage under 35 U.S.C. 371 ofinternational application PCT/IL99/00321, filed Jun. 14, 1999 whichdesignated the United States, and which international application waspublished under PCT Article 21(2) in the English language.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates generally to a method and apparatus forforming a metal plate. More specifically, the present invention relatesto a method and apparatus for cutting and perforating a metal plateoptionally accompanied by forming the plate into a three-dimensional(3-D) shape.

Metal plates of various sizes and thickness are a starting material forthe preparation of a variety of objects. Metal plates can be shaped toassume a 3-D shape, may be cut, perforated, etc. Cutting and perforationare achieved in the art by the use of presses, by the use of a laser,etc.

The invention, has at its object to provide a novel cutting andperforation method.

GENERAL DESCRIPTION OF THE INVENTION

The present invention is based on the realization and observation that ametal plate which is intensely forced against a surface with boundariesor openings defined by wall sections essentially normal to the plate andthus parallel to the direction of application of the force is cut alonglines defmed by said wall sections. In other words, the point ofintersection of said wall sections and said surface defines a shearingline and acts as a knife in such a process. Thus, in accordance with thepresent invention a metal plate is forced against a mold formed withsuch edges or openings, whereby edge portions (portions defined betweena cut line and the edge of the plate) may be cut away and openings (orperforations) formed within the plate. The force, by one embodiment, maybe a pulsed magnetic force. In accordance with another embodiment, theforce may be that generated by a shock wave generated in a fluid.

The present invention thus provides a method for forming a metal plate,comprising:

(a) providing a mold with a forming plane which in operation faces theplate, having at least one of openings or boundaries defined by wallsections extending essentially normal to said forming plane, edges ofsaid openings or boundaries defining shearing lines;

(b) placing the plate against said forming plane; and

(c) generating an abrupt and intense pressure pulse and applying it ontosaid plate to force it towards said mold, whereby said plate is cutalong said cut lines.

The present invention also provides an apparatus for forming a metalplate, comprising:

(i) a mold comprising a forming plane which in operation faces theplate, having at least one of openings or boundaries defined by wallsections extending essentially normal to said forming plane, saidopenings or boundaries defining cut lines; and

(ii) a device for generating an abrupt and intense force pulse and forapplying it onto said plate to force it towards said mold, to cut saidplate along said cut lines.

In accordance with one embodiment of the invention, said force pulse isa pulsed magnetic force (PMF). The PMF may be generated by a PMF devicecomprising one or more forming coils, which are typically concentric,placed opposite and proximal to the forming plane and extendingperipheral to its boundaries. Each forming coil is connected to anelectric discharge circuitry for discharging a short and intenseelectric current pulse through the forming coil to yield the PMF to formsaid metal plate.

A background on prior art apparatuses and methods for working of metalworkpieces by the PMF process can be found in U.S. Pat. Nos. 3,654,787,3,961,739, 4,170,887, 4,531,393, 4,807,731, 5,353,617 and 5,442,846, andin PCT Application Publication No. WO 97/22426.

In accordance with another embodiment of the invention, the force pulseis a result of a pressure pulse generated by the breakdown or dischargeof an intense electric current through a fluid of a discharge-in-fluid(DIF) device. A DIF device comprises a fluid basin and of electricdischarge electrodes embedded within the fluid, which are connected toan electric discharge circuitry for discharging a short and intenseelectric current within the fluid. The discharge generates an electricspark or breakdown within the fluid which yields the formation ofplasma, vapor or both and consequently a pressure wave. The fluid basinhas an opening, which may at times be sealed by a flexible membrane,which opening is close proximity, usually in contact with the plate.Thus, the abrupt pressure wave generated within the DIF device isthereby transmitted to the plate. The fluid in the basin is preferably aliquid, particularly an aqueous solution.

In accordance with vet another embodiment, the force pulse is a combinedPMF and a DIF generated force. For example, the actual portion of theplate may be formed by a DIF device, while peripheral portions with aPMF; through a forming coil disposed peripheral to a DIF device.

An abrupt and intense pressure may also be achieved by other means suchas, for example, by means of an explosive charge.

Where the mold comprises openings, holes will form in the plate atlocations corresponding to the openings. For example, where the plate isintended to be used as a satellite dish, such openings may be used asthrough holes for passing screws through the plate to fasten them to asupport structure.

Where the mold comprises said boundaries, edge portions of the plate arecut off along lines defined by said boundaries, with the cut boundariesthen defining edges of the formed plates.

As will no doubt be appreciated, at times, a plate may be simultaneouslycut along boundaries as well as perforated with holes. Furthermore,typically, the plate is simultaneously shaped to assume a 3-D shapedefined by a mold's contours and simultaneously cut along its edges andperforated.

In the case of a satellite dish, it is at times desired (particularlyfor structure reinforcement) to form a dish with a downward dependingperipheral skirt portion relative to its front plane. This requiresfirst bending of its peripheral edge portions and then trimming the bentedge portions so that the skirt will have a desired width. This feat isvery difficult to attain in accordance with the prior art. The inventionalso provides a method and apparatus for the formation of a dish withsuch a peripheral skirt. A method for forming a metal plate with adepending peripheral skirt portion, in accordance with this aspect,comprises:

(a) providing a mold having an overall annular shape and a formingplane, which in operation faces the plate, having rounded edges;

(b) placing the plate against said forming plane; and

(c) generating an abrupt and intense force pulse and applying it ontosaid plate to force it towards said mold, whereby said plate is formedto assume a 3-D shape corresponding to contours of the mold, while edgeportions with edge portions of the plate being bent about said roundededges; and

(d) applying a pulse magnetic force (PMF) onto said edge portion in adirection which is essentially normal to said edge portion against ashearing line defined between a face having said edge portion and a wallportion normal thereto, whereby said edge portion is cut along saidshearing line.

This aspect also provides an apparatus for forming a metal plate,comprising:

(i) a mold with a forming plane which in operation faces the plate,having rounded edges;

(ii) a device for generating an abrupt and intense force pulse in anaxis essentially normal to said forming plane and for applying it ontosaid plate to force it towards said mold and to force edged portions ofthe plate to bend about said rounded edges; and

(iii) an auxiliary pulsed magnetic force (PMF) device with an auxiliaryforming coil for applying a PMF pulse onto and in a directionessentially normal to the bent edge portion of the plate against an edgeportion retaining surface provided with shearing lines defined betweensaid surface and wall portions perpendicular thereto; in anedge-shearing state of the operation the bent edge portion is retainedbetween said surface and said auxiliary forming coil with said shearingline being opposite said auxiliary forming coil, whereby upon dischargeof current through said auxiliary forming coil, said edge portion is cutalong said shearing lines.

In accordance with one embodiment of the apparatus according to thislast aspect, the forming coil is associated with the mold, e.g. placedin a recess in an annular side wall thereof and the shearing line isdefined in an annular member which in said edge-trimming operationalstate is placed opposite said auxiliary forming coil. In accordance withanother embodiment, said shearing line is defined in side wall of themold and the forming coil is received within an edge-trimmingoperational state is placed opposite said shearing lines.

Said device for generating the intense force pulse may, in accordancewith one embodiment, be a PMF device with a forming coil or may be a DIFdevice.

The present invention is applicable to forming metal plates of differentshapes, of different metals, of different thickness, etc. As will beappreciated, the present invention is not limited to plates of anyspecific specification. The invention may be applied to large plates, toform relatively large objects, e.g. a satellite dish, and may also beapplied for forming small components. At times, a mold used may in factcomprise a plurality of sub-mold structures, each defined by boundariesfor the simultaneous preparation of a number of different objects from asingle plate. In addition, although the present invention is definedwith reference to the formation of a plate, it should be understood thatat times the object of the process may be the cut-off portionsthemselves, e.g. portions defined by said openings or the trimmedperipheral edge portions. Thus, for example, openings of a desired shapemay be used to define the shape of planar objects which are thus cut-offfrom the plate by the process of the invention.

In the following, the invention will be described in a non-limitingmanner with reference to the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematical cross-section through a forming apparatus inaccordance with an embodiment of the invention, prior to forming themetal plate.

FIG. 2 is a top elevation of the coil of the apparatus of FIG. 1.

FIG. 3 is a schematical representation of the combined process forshaping, cutting (edge portion-trimming) and perforating using thedevice of FIG. 1.

FIG. 4 is a cross-sectional view of a dish formed in the apparatus ofFIG. 1 and by the illustrated process.

FIG. 5A is a schematical cross-section through a forming apparatus inaccordance with another embodiment of the invention.

FIG. 5B shows the apparatus of FIG. 5A after the combined shaping,cutting and perforation to yield a formed dish.

FIG. 6 is a schematical cross-section through a forming apparatus inaccordance with another embodiment of the invention, prior to formingthe metal plate.

FIG. 7 is a schematic representation of the combined process forshaping, cutting (edge-trirnming) and perforating, using the device ofFIG. 6.

FIG. 8 is an enlarged cross-sectional view of the PDF electrode in theapparatus of FIG. 1.

FIG. 9 is an enlarged cross-sectional view of a PDF electrode inaccordance with another embodiment of the invention.

FIG. 10 is a schematic cross-section through a forming apparatus inaccordance with another embodiment of the invention prior to forming themetal plate.

FIG. 11 is a schematic, planar representation of a forming apparatus inaccordance with another embodiment of the invention.

FIGS. 12A and 12B are schematic illustrations of two alternativeelectric circuitries for discharging the rapid intense electric currentpulse through the PDF electrodes and through the forming coil in theapparatus of FIG. 6.

FIGS. 13A-13D show an apparatus in accordance with another embodiment ofthe invention for forming a satellite dish with a depending skirtportion in several successive stages of forming a dish with a skirt.

FIG. 13E shows the dish formed by the apparatus of FIGS. 13A-13D.

FIGS. 14A-14D show an apparatus in accordance with another embodiment ofthe invention for forming a satellite dish with a depending skirtportion in several successive stages of forming a dish with a.

FIG. 14E shows the dish formed by the apparatus of FIGS. 14A-14D.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Reference is first being made to FIG. 1 showing an apparatus generallydesignated 10, comprising a mold 12, a forming coil assembly 14 holdingbetween them a metal plate 16.

Mold 12 has a forming surface 18 of a generally circular shape withedges 20, defined by upright side walls 22 with a central domed-shapeddepression 24 and an annular groove 26. The dome-shaped depression hasopenings 27 defined by upright walls 28. As will be appreciated, thespecific shape of the mold which defines the shape of the dish to beformed in the apparatus is an example only and it may assume also avariety of other shapes. By way of illustration, the mold may have anoverall rectangular shape, may have different kinds of depressions forforming dishes with different three-dimensional patterns, etc. Thus thespecific illustrated embodiment does not derogate from the generality ofthe invention as defined herein.

Mold 12 is surrounded by an annular member 32 which has an upper surface34, below edge 20, and having a chamfered inner portion 36 for receivingand holding sheared material waste (see below).

Coil assembly 14 consists of a coil 40, embedded within space 41, formedat the bottom of a supporting block 42. Block 42 is preferably made of anon metallic substance. Coil 40 should be electrically insulated fromsurrounding metal objects, particularly metal plate 16, for whichpurpose space 41 may be filled by an electrically insulating material oralternatively coil 40 may be covered by an electrically insulatingmaterial.

Coil 40 is electrically connected to an electric discharge circuitry 50comprising a capacitor battery 52 and a high current rapid dischargeswitch 54, both as known per se. An example of such a discharge switchis a controlled vacuum discharger such as that disclosed in ApplicationNo. PCT/IL97/00383. Switch 54 is controlled by a control circuitry 55.

Metal plate 16 is generally planar and has boundaries such that itextends beyond edges 20 of mold 12.

In operation, as illustrated in FIG. 3, switch 54 is closed, wherebyelectric current rapidly discharges through coil 40 yielding a pulsedmagnetic force which induces a very rapid movement in portions of plate16: portions overlaying depression 24 and annular groove 26 are deformedto assume a three-dimensional shape defined thereby and peripheral edgeportions 60 of plate 16 are sheared over peripheral edges 20 of the mold12. In addition, when the portion 29 of the plate impacts the bottomwalls of depression 24, small portions 44 are cut-off from portion 24,leaving holes 46 of a diameter corresponding to that of openings 27.Portions 44 continue to move through openings 27 and are therebydischarged. Thus, a dish 62 as shown in FIG. 4, having a central concavedepression 64 with holes 46 and a planar edge portion 66 with an annulargroove 68 is thereby formed. Such a dish is useful, for example, as anantenna, in particular such used in satellite communication. Annularmember 32 can then be pushed upwards to allow disposal of shearedportion 60.

Reference is now being made to FIGS. 5A and 5B showing an apparatusgenerally designated 80 in accordance with another embodiment of theinvention. The apparatus comprises a mold 82 with openings 83 and aforming coil assembly 84 with a coil 85 holding between them a metalplate 86. A discharge circuitry 88 is connected to coil 85. A majordifference between apparatus 80 of FIGS. 5A and 5B and apparatus 10 ofFIG. 1 resides in that the mold, rather than being concave is convex.Otherwise, the operation of the apparatus is essentially similar to thatdescribed with reference to FIGS. 1-3 with FIG. 5B illustrating theapparatus after dish 90 with edges 91 has been formed from plate 86leaving behind an annular trimmed edge portion 92 and small cut-offportions 93 which are expelled through openings 83. As the process isessentially the same as that described with reference to FIGS. 1-3 thedescription will not be repeated again and the reader is referred to thedescription above.

Reference is now being made to FIG. 6 showing an apparatus generallydesignated 110 comprising a mold 112 and a force generating assembly 114holding between them a metal plate 116.

Mold 112 has a forming surface 118 of a generally circular shape withedges 120 defined by upright walls 122, a central dome-shaped depression124 with openings 123 and an annular groove 126. Similarly as in thecase of FIG. 1, the specific shape of the mold which defines the shapeof the dish to be formed in the apparatus is an example only and it mayassume also a variety of other shapes. By way of illustration, the moldmay have an overall rectangular shape, may have different kinds ofdepressions for forming dishes with different three-dimensionalpatterns, etc. Thus the specific illustrated embodiment does notderogate from the generality of the invention as defined herein.

Mold 112 is surrounded by an annular member 132 which has an uppersurface 134, at a distance from planar surface 118, and having achamfered inner portion 136 for receiving and holding sheared materialwaste (see below).

Force generating assembly 114 comprises a PMF device, generallydesignated 140 comprising a fluid basin 142 holding fluid 143 havingdisposed therein a plurality of discharge electrodes 144 (two are shownin this cross-section but it can be appreciated that a larger number atvarying locations within the basin may be provided). Fluid 143 istypically, but not exclusively a liquid, typically an aqueous solution.Fluid 143 may also, at times, be a gas. The basin has an opening 146sealed by a flexible planar wall 48 extending over and fixed to edges150 of the opening (the manner of fixing may be as known per se and isnot shown).

The size of opening 146 is such so that it is opposite the majordepression 124 of the mold and preferably also opposite otherdepressions, such as depression 126.

Force generating assembly 114 further comprises a planar coil member 152arranged so as to define a frame around opening 146 and has a face 154which faces the metal plate which is in close proximity to metal plate116. The position and size of coil member 154 is such so that it isopposite portion of plate 116 including such portions which are oppositeedge 120 and extending peripherally therefrom. As will be appreciated,the forming coil 156, within forming coil member 152, should preferablybe electrically insulated both from plate 116 as well as from otherelectrically conducting objects, such as the body of device 140 in casethis is made of metal or another conducting substance. It is to benoted, however, that the body of the device is preferably made of anon-metallic rigid substance, of a rigidity such that it can withstandthe pressure generated within basin 142) and accordingly it may beembedded in or covered by an electrically insulating material.

Electrodes 144 and forming coil 156 are electrically connected to anelectric discharge circuitry 160.

Referring now to FIG. 7, upon activating of electric circuitry 160,current is simultaneously discharged through electrode 144 and coil 156.The discharge through electrodes 144 yields generation of a spark withinbasin 142, causing plasma and vapor formation in liquid 143. This givesrise to a pressure wave applying pressure on flexible wall 148 whichthereby deforms the central portion of metal plate 116 into thedepression 124. Upon impact with the walls of the depression portions160 are cut-off and expelled through openings 123, leaving behind holes162 in the plate. The electric discharge through coil 156 gives rise toa pulsed magnetic force in the peripheral portions of the plate shearingthese peripheral portions 184 off. Thus, a dish similar to that of FIG.4 is formed.

A schematic representation of the structure of electrode 144 is shown inFIG. 8. Electrode 144 is formed from a metal tube with a lumen 166having a tapered discharge end 168. The electrode is coated by anelectrically insulating layer 170. Lumen 166 is connected to a gassource, e.g. air, which is supplied by a compressor or a compressed gasreservoir (not shown). Such gas is allowed to sip into basin 142facilitating the generation of electric discharge and the formation ofplasma within liquid 143 (typically an aqueous solution) contained inbasin 142. In some embodiments of the invention the electrode maycomprise a single conductivity (non-gas transmitting) tip.

In the case of electrodes of the kind shown in FIG. 8, or electrodescomprising a single conducting tip, each pair of electric dischargemembers is constituted by two electrodes.

Another embodiment of an electrode 172 in accordance with the inventioncan be seen in FIG. 9. The electrode 172 of this embodiment, is aco-axial electrode with a central electrode member 174 and a peripheralannular electrode member 176, the two being isolated by an electricallynon-conducting layer 178. Members 174 and 176 are connected to adischarge circuitry 180. In this way, upon discharge of the intense andrapid electric current pulse, a spark will be generated between pole 174and pole 176.

It should be noted, that in some other embodiments, the body of thebasin 182 may form one of the discharge members of a discharge pair andthus the discharge will be between an electrode and the body.

An apparatus 190 in accordance with another embodiment of the inventioncan be seen in FIG. 10. The apparatus 190 differs from apparatus 10shown in FIG. 1 in that (i) it does not comprise a flexible wall andthus the fluid within the basin is in direct contact with the metalplate; and (ii) in that it does not comprise a peripheral shearing coil.In the case of apparatus 190 the pressure wave generated within theliquid hits the plate directly causing it to deform and shearing itsperipheral portions. Furthermore, the mold in this device does not haveopenings. Rather, it is provided with a plurality of vacuum ducts 192leading from the space within depression 196 to a vacuum source (notshown) which draws gas therefrom (represented by arrows 198).

Reference is now being made to FIG. 11 showing an apparatus generallydesignated 230 comprising a fluid basin 232 with a plurality ofelectrodes 234, 236, 238 and 240. Each pair of electrodes (234, 236,etc.) being connected to a corresponding discharge circuitry 242, 244,246 and 248, respectively, which are under control of a controlcircuitry 250.

An electric current is discharged between each pair of electrodes andcan be timed such that all discharges will be simultaneous or such thatcurrent will be discharged through different pairs in a predeterminedsequence.

Two embodiments of electric discharge circuitries 260A and 260B, areshown in FIGS. 12A and 12B, respectively. Discharge circuitry 260Acomprises an electric power source 270, which may be a capacitor or abank of capacitors, a high current rapid discharge switch 272, e.g. acontrolled vacuum discharger (which may be any such device known per se,or such as that disclosed in PCT Application No. PCT/IL97/00383) and atriggering unit 274 which actuates discharge of switch 272. The switchand the power source are connected in series with forming coil 254 andwith electrodes 244 embedded within basin 242. The electric dischargecircuitry is typically grounded at 280. Upon triggering by trigger units274, switch 272 closes, thus giving rise to current discharge throughcoil 253 in electrodes 244.

In the case of the alternative electric circuitry 260B rather thanhaving coil 254 and electrodes 244 connected in series, there areprovided two parallel circuits 282 and 284, the first for dischargingcurrent through coil 254 and the latter for generating electricdischarge through electrodes 244 within basin 242. The electric switches270′ and 270″ in the two circuitries are triggered in parallel by atriggering unit 274′. Both electric circuitries 282 and 284 have theirindependent power source 270′ and 270″. Electric circuitry 260B shown inFIG. 5B is useful in the case of an impedance mismatch between theelectrodes and the coil.

Reference is now being made to FIG. 13A showing an apparatus generallydesignated 300 comprising a mold 302 and a primary forming coil assembly304, holding between them a metal plate 306. Mold 302 has a formingplane 308 with a central inverted dome-shaped depression 310, roundededges 312, and essentially upright annular side walls 314. Receivedwithin an annular groove 316 of the side walls is an auxiliaryedge-trimming coil 318 connected to a discharge circuitry 320 which isunder control of control unit 322. As will be appreciated, where mold302 is made of metal, it is necessarily to properly isolate coil 318therefrom.

Coil assembly 304 consists of a primary coil 330 contained in a coilholding receptacle 332 within a coil support block 334. Here again, aswill be appreciated, it is necessary to ensure proper isolation of coil330 from both block 334, if made of metal, and plate 306. Coil 330 isconnected to a discharge circuitry 338 controlled by control unit 340.As will be appreciated, control mechanism 340 may be combined withcontrol mechanism 322.

As illustrated in FIG. 13B, upon discharge of electric current throughcoil 330, the magnetic force forces plate 306 towards the mold, wherebythe central portion 350 assumes the shape of depression 310 while theedge portions 352 bend over the rounded edges 312.

At the next stage of the process, illustrated in FIG. 13C, coil assembly304 is removed and a body 340 having upright downwardly extendingannular members 342 with a right angled shearing edge 344 definedbetween face 346 and wall portion 348 is brought instead. Body 340 islowered over the mold in a direction represented by arrow 358. Thiscauses the forced bending of edge portions 352 as represented by arrows360 to reach the stage as illustrated in FIG. 13D. Then, as alsorepresented in the last figure, current is discharged through edgetrimming coil 318 generating a magnetic force in a direction representedby arrows 364 thus shearing the peripheral edged portion 366 representedby dashed lines in FIG. 13D. After removal of body 340 the edge portionssomewhat recoil. Thus, a formed plate 370 with a central recess 372 andan annular skirt portion 374, as seen in FIG. 13E, is formed.

An apparatus 400 in accordance with another embodiment, also useful forforming a plate with an annular skirt portion, and the process offorming using this apparatus, is seen in FIGS. 14A-14D. Referring firstto FIG. 14A, the apparatus comprises a mold 402 with a centraldepression 404 and rounded edges extending downward to an annularshearing edge 408 defined between the annular side wall of the mold 410and laterally extending wall portion 412. The apparatus also comprises aprimary forming coil assembly 420 with a coil receptacle 422 holding aprimary forming coil 424, with the coil connected to a dischargecircuitry 430. Held between mold 402 and forming coil assembly 420 is ametal plate 436.

After discharging of current through forming coil 424, plate 436 isshaped, in a similar manner to that represented in FIG. 13B, to assume ashape as shown in FIG. 14B, with edge portions 438 bent about roundededges 406 extending below shearing edge 408. After this step, theforming coil assembly 420 is removed and replaced by a forming coilholding assembly 450 with downwardly projecting annular member 452holding within a recess 454 formed in an inner face thereof; anauxiliary forming coil 456. The auxiliary forming coil 456 is connectedto a current discharge and control circuitry 458.

Upon association of assembly 450 and mold 402 with the initially formedplate 436, the edge portion 438 of the plate is further bent, in amanner analogous to that of FIGS. 13C-13D, and the auxiliary coil 456comes to lie opposite the sharing edge 408. Upon discharge of currentthrough forming coil 456 the peripheral edged portion 438 is shearedover shearing edge 408. Additionally, this PMF also forces the remainingpart of the edge portion against the side wall of the mold to assume ashape defined by its contours. Thus a formed plate 460, as seen in FIG.14E with a central recess 462 and an annular skirt 464 is formed.

What is claimed is:
 1. A method for forming a metal plate (306, 436)comprising: (a) providing a mold having an overall annular shape and aforming plane, which in operation faces the plate and which has roundededges; (b) placing the metal plate against said forming plane; (c) bymeans of a rapid and intense electric current pulse discharged from acapacitor battery of a power source generating an abrupt and intenseforce and applying it onto said plate to force it towards said mold,whereby said plate is formed to assume a 3-D shape corresponding tocontours of the mold while edged portions of the plate being bent aboutsaid rounded edges; and (d) applying through an auxiliary pulsedmagnetic force (PMF) device with an auxiliary forming coil, a PMF forceonto said edge portion in a direction which is essentially normal tosaid edge portion against a shearing line defined between a face havingsaid edged portion and a wall portion normal thereto, whereby said edgeportion is cut along said shearing line.
 2. A method according to claim1, wherein the formed metal plate is a satellite dish.
 3. An apparatusfor forming a metal plate comprising: a mold with a forming plane whichin operation faces the plate, having rounded edges; a device comprisinga power source with a capacitor battery that can generate a rapid andintense electric current discharge that in turn causes the generation ofan abrupt and a intense force pulse in an axis essentially normal tosaid forming plane that is applied onto said plate to force it towardssaid mold and to force edge portions of the plate to bend about saidrounded edges; and an auxiliary pulsed magnetic force (PMF) device whichhas an auxiliary forming coil for generating a PMF onto and in adirection essentially normal to the bent edge portions of the plateagainst an edged portion retaining surface provided with shearing linesdefined between said surface with both portions perpendicular thereto;in edge-shearing state of the apparatus the bent edge portion isretained between said surface and said auxiliary forming coil with saidshearing line being opposite said auxiliary forming coil, whereby upondischarge of current through said auxiliary forming coil, said edgedportion is cut along said shearing lines.
 4. An apparatus according toclaim 3, wherein said auxiliary forming coil is associated with saidmold and the shearing line is defined in an annular member, which insaid edge-trimming operational state is placed such that said shearingline is opposite said auxiliary forming coil.
 5. An apparatus accordingto claim 3, wherein said edge shearing line is defined in side walls ofmold and the forming coil is received within auxiliary coil-holdingmember which in the edge shearing operational state of the device is ina position such that said auxiliary coil lies opposite said shearingline.